Descent to the Underworld is a Single Player level in Q2. This level has the same geometry as Underworld Prey, though placement of Weapons is somewhat different as the only weapons are a Grenade Launcher and Nailgun placed on two shelves. A custom message exists when the player picks up the Nailgun, unlike in Underworld Prey, that says "Groovey!".
Turn around and enter the room behind you. Kill the 2 Grunts. An Elevator exists here, but it is one-way and won't let you descend. Return to the starting room and ignore the room on the opposite side, instead going down the staircase to the left of that doorway. At the bottom, turn around and kill the Grunt underneath the stairs. Go to the right side of the room to pick up a Grenade Launcher and Nailgun on the two shelves. Picking up the Nailgun will get a message saying "Groovey!". In between the shelves is a mantle that can be leaped to by either of the shelves. Upon climbing this, turn around to face the room. You should notice a box exists in the middle of this room with a small window on the side you are looking at. Inside is a Scrag that you can kill. Enter the room in front of you and kill the 4 Rottweilers. Return to the previous room and enter the doorway on the opposite side. Kill the 2 Grunts and ride the Elevator, this is the same one that you saw earlier. Return to the first room and go into the doorway you previously ignored. A hole in the floor looks down into the room with the 4 Rottweilers. Ascend up the Elevator to your right to the next floor and turn around at the top. Turn left and kill the 2 Grunts in the long corridor. A hole on your side of the corridor overlooks the room with the hole. Continue down the corridor to the end. Dropping in this hole would lead to the first to second floor Elevator.
- A message is supposed to appear when picking up the Grenade Launcher - "Who wants some?". This does not appear in-game due to the command that would call it up, called "message", being misspelled "messaage".
- The level has a Double-Barrelled Shotgun, 2 Nailguns, a Super Nailgun, a Grenade Launcher, and a Rocket Launcher that do not spawn due to being intended only to appear in Multiplayer games. As there are no spawn locations for Multiplayer games, this means it is normally impossible to access these weapons.
- All unused Weapons would have had custom pickup messages: